Generally, rotary atomizing head type coating apparatuses have a rotary atomizing head mounted on a rotational shaft of an air motor. In rotary atomizing head type coating apparatuses of this sort, it has been known to provide a feed tube internally of the rotational shaft to supply paint or cleaning fluid toward a rotary atomizing head (e.g., see, for example, Japanese Patent Laid-Open No. H10-156224 and 2002-186883).
In the prior art as mentioned above, a rotary atomizing head is formed in a bell or a cup like shape, and composed of a main atomizer body (a main body of a rotary atomizing head) having a paint reservoir at the depth on a concave front side, and a paint spreading surface which paint is spread into the shape of a thin film in front of the paint reservoir, and a partition member located on the inner peripheral side of the main atomizer body to partition off the paint spreading surface from the paint reservoir and provided with paint outlet holes to let paint flow out onto the paint spreading surface from the paint reservoir.
Japanese Patent Laid-Open No. H10-156224 discloses a main body of a rotary atomizing head which is provided with a solvent passage to communicate a paint reservoir with an outer peripheral side of a main atomizer body, for the purpose of washing outer peripheral surfaces of the rotary atomizing head. However, in this case, there is a problem that part of paint in the paint reservoir flows into the solvent passage and then onto the outer peripheral side of the main atomizer body through the solvent passage.
In contrast, Japanese Patent Laid-Open No. H8-332415 and 2002-186883 disclose a main atomizer body having a solvent reservoir which is provided separately from the paint reservoir and located on the rear side of the paint reservoir for the purpose of pooling there a solvent (a wash fluid) like thinner. In this case, by way of a solvent passage, the solvent reservoir is communicated with the outer peripheral side of a main atomizer body, i.e., a main body of the rotary atomizing head. At the time of washing the rotary atomizing head, a solvent is fed to the solvent reservoir on the main atomizer body when the rotary atomizing head is put in high speed rotation. Under the influence of centrifugal force, the solvent in the solvent reservoir is urged to flow out onto the outer periphery of the main atomizer body through the solvent passage to wash outer peripheral surfaces of the main atomizer body.
By the way, in the case of the prior art rotary atomizing head type coating apparatus which has a solvent reservoir provided on a main atomizer body in addition to a paint reservoir, it is inevitable that the main atomizer body is increased in size to make it. Therefore, it is difficult to manufacture a compact coater unit for use in a narrow limited space, in addition to a problem that the rotary atomizing head becomes so complicated in construction as would incur a higher production cost.
Furthermore, a solvent in the solvent reservoir on the main atomizer body is supplied to the outer peripheral side of the main atomizer body under the influence of centrifugal force by the rotary atomizing head which is put in high speed rotation. Accordingly, when the rotary atomizing head is at a rest, it is difficult to wash outer peripheral surfaces of the main atomizer body because no centrifugal force acts on the solvent in the solvent reservoir.